A spiral line pulse generator is disclosed by R. A. Fitch, et al in U.S. Pat. No. 3,289,015, issued Nov. 29, 1966. The generator is a device capable of storing electrical energy and, upon momentary short circuiting of a pair of terminals associated with the device, of providing a high amplitude pulse. The spiral line pulse generator, when properly utilized, provides the dual function of energy storage and voltage multiplication. The spiral line pulse generator is a transient field reversal device that provides an approximately triangular pulse. Its peak voltage is a multiple of the initial charging voltage. The construction of the spiral line is such that the voltage from the beginning to the end of the line adds through vector inversion producing a very high voltage pulse.
Some arc discharge lamps are known to be particularly difficult to start. One example of such a lamp is an arc lamp containing a sodium amalgam and a noble gas such as xenon at a relatively high pressure, such as 500 Torr. Another example of a difficult lamp to start is a metal halide lamp which requires a higher starting voltage than is available from an AC voltage line, of a wide range of voltages, with the use of a simple ballast.
The use of a spiral line pulse generator to start high pressure sodium lamps is disclosed in U.S. Pat. No. 4,325,004 to J. M. Proud, et al issued Apr. 13, 1982 and assigned to the assignee of the present application. In this patent, the output of the spiral line pulse generator is coupled to a conductor or starting aid, located in close proximity to an outer surface of the discharge tube. In the case of metal halide lamps, it has been found undesirable to locate conductors in close proximity to the central portion of the discharge tube, thereby ruling out the use of a starting aid to assist in initiating discharge in metal halide lamps.
U.S. Pat. No. 4,353,012 to C. N. Fallier, Jr. et al, issued Oct. 5, 1982, and also assigned to the assignee of the present application, shows a starting circuit for high intensity discharge metal halide lamps which comprises a spiral line pulse generator including two conductors and two insulators, each in the form of an elongated sheet, constructed in an alternating and overlapping arrangement which is rolled together in a spiral configuration having a plurality of turns. The spiral line pulse generator includes an output terminal coupled to one of the electrodes of the lamp and a pair of input terminals. One of the input terminals and the other of the electrodes of the lamp are adapted for coupling to a source of lamp operating power for delivering lamp operating power, received from the source, through the spiral line pulse generator to the discharge lamp. The starting circuit includes a spark gap and series resistor for applying a voltage between the conductors of the spiral line pulse generator and for switching the generator from a first voltage to a second voltge in a time interval much shorter than the transit time of electromagnetic waves through the spiral line pulse generator. After operation of the spark gap switch, the spiral line pulse generator provides, at its output terminal, a high voltage, short duration pulse of sufficient energy to initiate discharge in the discharge lamp.
While the starting circuit described in U.S. Pat. No. 4,353,012 is suitable for the purposes intended, its performance could be improved substantially if greater output voltage could be applied to the lamp electrodes, producing a higher starting voltage and, thus, more reliable lamp starting.